Use a ruler or measuring tape
Measure when the penis is fully erect for the most consistent result
Place the ruler on the top side of the penis
Press the ruler gently into the pubic bone at the base
Measure from the pubic bone to the tip of the glans
Do not include the foreskin in the measurement
For girth, wrap a measuring tape around the thickest part of the shaft
Record the measurement in inches or centimeters
Measure more than once and use the same method each time